The present invention concerns a feeding means serving to feed into a solid fuel-using heating boiler, solid fuel from a storage silo or equivalent, said feeding means comprising a piston means disposed to move reciprocatingly in a tube means communicating by an aperture with the solid fuel storage silo or equivalent and communicating by its other end with the heating boiler.
As a consequence of the continuous increase in price of oil, the use of solid fuel, such as wood chips, peat etc., is increasing at an accelerating rate in heating energy generation. Several different types of chipping machines for chip production are known. The operation of conventional chippers is based on a rotating drum-like roll which serves as blade and against which the wood is radially fed by the aid of separate feeding means. Such chippers require a high power input, whereby the producing of chips involves comparatively high expenditure.
It has been found that larger sized chips, or so-called lump chips, are better suited owing to their properties to be used towards heat production, compared with the above-mentioned common chips. To the purpose of lump chip producing, a lump chipper has been disclosed in the Finnish patent application No. 791491, comprising a rotating, conical screw. The helical surface of this screw acts as cutting blade and it provides the feeding of the wood, in addition to the chipping operation.
One advantage which lump chips have over conventional chips is that when stored in a heap, lump chips dry out because the air is able to pass through between the lump-shaped wood pieces. In contrast, conventional chips are too closely packed, whereby the burning of the wet chips in a boiler causes difficulties and extra costs, in addition to which the wet chips have a low calorific value.
At present, the feeding of lump chips into a heating boiler is accomplished by manual labour in that lump chips are shoveled into the furnace of the boiler as required. Quite obviously this problem solution is not satisfactory. In addition, the shovelling done as human labour is rather strenuous work.
Attempts have been made to find an appropriate apparatus solution for the feeding of lump chips, but these attempts have not met with any success so far. One has tried to use for the feeding of lump chips, a screw conveyor (as has been disclosed e.g. in the German publicizing print No. 2 821 767), but a feeding means of this type does not constitute any satisfactory solution.
Solid fuel has been fed from a storage silo or equivalent into a solid fuel-using heating boiler with the aid of so-called piston feeding means. Such a feeding means is disclosed e.g. in the Finnish Pat. No. 40187, in the Swedish Pat. No. 32.806 and in the German Pat. No. 74.080. This piston means of prior art comprises a piston in reciprocating motion, fitted into a passage which through an aperture communicates with a solid fuel storage silo or equivalent. The drawback encumbering these piston feeding means of prior art is that the solid fuel cannot be made with positive reliability to go from the storage silo or equivalent before the piston of the piston feeding means, owing to the vaulting tendency of the solid fuel.